Optical fiber based surface sensing system that enables spectral multiplexing

Abstract

A surface sensing system including at least two sensors located on the end of the same optical fiber. The sensors are configured such that they exhibit resonant frequencies or Q-factors that are distinguishable from each other, where the Q-factor is defined as the resonant frequency divided by the resonance spectrum at full-width half maximum (FWHM). Because the sensors have distinguishable resonant frequencies or Q-factors and are located on the end of the same optical fiber, they can be monitored in parallel with little or no optical interference.

1. A sensor comprising:
 an optical fiber having an end; 
 a first sensor located on the end of the optical fiber; and 
 a second sensor located on the end of the optical fiber; 
 wherein the first and second sensors are configured such that the first and second sensors exhibit resonant frequencies or Q-factors that are distinguishable from each other. 
 
   
   
     2. The sensor of  claim 1  wherein the first sensor has a spatial profile of regions of high and low dielectric constant that results in a first resonant frequency and Q-factor and wherein the second sensor has a spatial profile of regions of high and low dielectric constant that results in a second resonant frequency and Q-factor. 
   
   
     3. The sensor of  claim 2  wherein the spatial profiles of the first and second sensors include patterns of low dielectric constant features. 
   
   
     4. The sensor of  claim 3  wherein the low dielectric constant features of the two sensors are at a different pitch. 
   
   
     5. The sensor of  claim 2  wherein an aspect of the spatial profile of the first sensor is different from the same aspect of the spatial profile of the second sensor. 
   
   
     6. The sensor of  claim 1  wherein the first and second sensors cover non-overlapping portions of the optical fiber end. 
   
   
     7. The sensor of  claim 1  further comprising a spectral multiplexing system in optical communication with the optical fiber configured to enable parallel detection of an optical signal that interacts with the first and second sensors. 
   
   
     8. The sensor of  claim 7  wherein the spectral multiplexing system includes a tunable laser source wherein the wavelength range of the tunable laser source includes the resonant frequencies of the first and second sensors. 
   
   
     9. The sensor of  claim 1  further comprising a spectral multiplexing system in optical communication with the optical fiber, the spectral multiplexing system having an optical signal source configured to provide a swept optical signal to the optical fiber and a detector configured to detect portions of the optical signal that interact with the first and second sensors. 
   
   
     10. The sensor of  claim 1  wherein the first and second sensors are fabricated on the end of the optical fiber. 
   
   
     11. A method for characterizing one or more physical properties of a test medium, the method comprising:
 exposing first and second sensors to a test medium, wherein the first and second sensors are located on the end of the same optical fiber and configured such that the first and second sensors exhibit resonant frequencies or Q-factors that are distinguishable from each other; 
 injecting an optical signal into the optical fiber such that the optical signal interacts with the first and second sensors in parallel; and 
 detecting the optical signal after it has interacted with the first and second sensors. 
 
   
   
     12. The method of  claim 11  wherein the optical signal has a broadband optical energy spectrum that includes the resonant frequencies of the first and second sensors. 
   
   
     13. The method of  claim 11  wherein the optical signal has a narrowband optical energy spectrum, the method further comprising sweeping the optical signal across a range of wavelengths that includes the resonant frequencies of the first and second sensors. 
   
   
     14. The method of  claim 13  wherein the detecting comprises detecting the optical signal with a single optical detector. 
   
   
     15. The method of  claim 11  further including monitoring shifts in the resonant frequencies associated with the first and second sensors. 
   
   
     16. The method of  claim 11  wherein the detecting comprises detecting the optical signal with a single optical detector. 
   
   
     17. A sensor system comprising:
 an optical fiber having an end; 
 a first sensor located on the end of the optical fiber; 
 a second sensor located on the end of the optical fiber, wherein the first and second sensors are configured such that the first and second sensors exhibit a distinguishable difference in at least one of resonant frequency and Q-factor; and 
 a spectral multiplexing system in optical communication with the optical fiber, the spectral multiplexing system having an optical signal source configured to provide an optical signal to the optical fiber and a detector configured to detect portions of the optical signal that interact with the first and second sensors. 
 
   
   
     18. The sensor system of  claim 17  wherein the first and second sensors have spatial profiles of regions of high and low dielectric constant that include patterns of low dielectric constant features. 
   
   
     19. The sensor system of  claim 18  wherein the low dielectric constant features of the two sensors are at a different pitch. 
   
   
     20. The sensor system of  claim 19  wherein the first and second sensors cover non-overlapping portions of the optical fiber end.